JP5495841B2

JP5495841B2 - Camera and camera control method

Info

Publication number: JP5495841B2
Application number: JP2010035970A
Authority: JP
Inventors: 泰則工藤
Original assignee: オリンパスイメージング株式会社
Priority date: 2010-02-22
Filing date: 2010-02-22
Publication date: 2014-05-21
Anticipated expiration: 2030-02-22
Also published as: CN102164247B; US20110206360A1; US8295697B2; CN102164247A; JP2011172145A

Description

The present invention relates to a camera and a camera control method .

For example, for the purpose of multi-functionality, a live view function that enables composition confirmation, etc., by continuously displaying an image formed on the image sensor, and continuously capturing and recording the image formed on the image sensor The video camera function is installed in the digital camera.

In order to display and record these continuous images with appropriate brightness, it is necessary to control the electronic shutter speed, aperture, and sensitivity in accordance with the change in luminance of the subject to keep the image brightness appropriate.

However, in exposure control by electronic control such as electronic shutter and sensitivity control, the control change is completed at the time of switching to the next screen of the movie, so the exposure can be set as intended for each frame. Since the aperture control with proper driving takes time, the relationship between subject brightness, aperture value, shutter speed, and sensitivity will be disrupted, resulting in the occurrence of frames with improper exposure, and image quality in live view display and video recording Will be dropped.

In response to this technical problem, a camera for recording moving images uses an aperture mechanism optimized for moving images. That is, it is a technique of preventing flickering by adopting a configuration in which the aperture can be switched in a stepless manner and slowly changing over time to reduce the luminance fluctuation amount per time.

FIG. 1 shows aperture control when a stepless aperture is used. A vertical synchronizing signal for controlling the image sensor is assumed to be VD. The operation of capturing one screen starts at the rise timing of VD.
The integration period is a time for accumulating the electric current output when the pixels of the image sensor receive light, and is an exposure time for imaging.

FIG. 1 shows an example in which the aperture is slowly changed from F5.6 to F4 over several frames.
In this way, if the speed is changed slowly, the error during driving of the aperture is suppressed to a minute level by feedback control that controls the shutter and sensitivity in the direction that cancels the minute change in the next frame by the minute change due to the aperture. Exposure amount obtained.

However, in still image shooting, good response (that is, reduction of the release time lag) is always required.

It is required to respond quickly to the brightness variation of the subject and always display it with proper exposure. However, when the aperture is moved slowly, the camera cannot follow if the subject has a large brightness variation in a short time. There is a technical problem that it takes time until the image is displayed by exposure, and a photo opportunity is missed.

Furthermore, since the aperture of the taking lens designed for still images is required to be driven quickly from the viewpoint of reducing the release time lag, the aperture drive is generally step-driven.

When a lens having a step-driven aperture specialized for still image shooting is used in a moving image, the operation is as shown in FIG. That is, when changing the aperture at the third rise of the vertical synchronizing signal VD from the left, since the exposure is suddenly changed during the integration of imaging, the brightness of the image during this integration period becomes unstable.

That is, when shooting a movie with a lens specialized for still image shooting, the exact aperture value during driving of the aperture is unknown, and if the AV value is changed greatly, the image will become brighter for a moment and the live view image will look good. In a still image lens that deteriorates, a photometric value cannot be measured during aperture driving, and thus there are technical problems such as an AV value becoming unknown.

For example, in the example of FIG. 2, consider a case where the aperture is opened from AV5 to AV4.5. Assuming that the subject brightness is very small and the level of change can be ignored, the shutter speed needs to be increased by 0.5 steps after the aperture drive than before the aperture drive.

However, the aperture value is indefinite during the aperture drive, so if the shutter speed and sensitivity are in the state before the aperture drive, an abnormally bright image is displayed on the monitor or a movie is recorded in the frame during the aperture drive. become.
Due to such technical problems, when a lens for still images is attached, a single-lens camera for still images that does not change the aperture during moving image recording is common.

In live view in which the imaging output is always displayed on the monitor and the composition can be confirmed, the technical problem as shown in FIG.

As a countermeasure for this technical problem, there is a process of displaying an image of the previous frame without displaying or recording an image that has been misaligned during driving, or a process of controlling at the maximum aperture as much as possible. It is common.

Further, FIG. 2 shows that a correct photometric value cannot be obtained during driving of the aperture with a camera having such an aperture. In this camera, photometry is not performed during driving of the aperture. The exclusive control of restarting the photometry after the aperture driving is performed.

The following prior art is known as a countermeasure for moving image shooting in a camera using an interchangeable lens having a step type aperture.
In Patent Document 1, the number of aperture stages used for moving image shooting when a silver salt film lens is mounted is made smaller than the controllable aperture stage number, and the number of aperture stages driven during moving image shooting is increased. A technique for obtaining an operation is disclosed.

As described above, if the number of stages of aperture control is roughened, the frequency can be expected to be reduced because the number of aperture fluctuations in the predetermined control range is reduced, but when driving the aperture, the exposure deviation due to driving the aperture is large and flickers. There is another technical challenge to grow.

In another patent document 2, two points are set at the shutter speed, and when the subject becomes bright, the aperture is driven to the side where the aperture is stopped when the shutter speed is high, and when the subject becomes dark, the aperture is opened at the point of the low-speed shutter. By providing hysteresis, the aperture frequently operates due to minute brightness fluctuations of the subject at the brightness point to drive the aperture, and the operation sound of the aperture drive mechanism is recorded as noise in the video shooting sound. I am trying to solve a technical problem.

JP 2002-290828 A JP 2004-056699 A

FIG. 3 is a program diagram showing the relationship among aperture driving, shutter speed, and luminance when no hysteresis is provided. The high-speed shutter is TV6 and the low-speed shutter is TV5. The sensitivity is constant at SV5 for the sake of simplicity of explanation.

FIG. 4 shows the relationship between the brightness and the movement of the diaphragm when such control is performed. When changing the aperture by one step with subject brightness BV4, if the subject always has a luminance variation of 0.1 step due to human movement, the aperture moves every 0.1 step, so the brightness becomes unstable. Become.

Therefore, when the method of Patent Document 2 is used, the high speed shutter point is set to TV7 and the low speed shutter point is set to TV5 as shown in the program diagram of FIG. Thus, a hysteresis that changes so that the AV value differs between the increase direction and the decrease direction of BV corresponding to the fluctuation of one level of luminance is configured.

With this configuration, once the aperture is set to AV3 at BV4, the aperture does not return to AV4 unless the aperture is brighter by one step from BV4, so the frequency of changing the aperture can be reduced.

However, when the aperture is driven, the change in one step means that the exposure is shifted up to one step during the aperture driving shown in FIG. 2, and the technical problem that the appearance of the moving image deteriorates at that moment still remains.

When the hysteresis is configured to be small, in addition to the direction in which the diaphragm is driven more frequently, if the subject brightness changes by one stage, the diaphragm is also driven by about one stage.
7 and 8 show examples of program diagrams in the case where a 0.5-stage hysteresis is configured.

If the luminance variation is about 0.5 steps, the aperture driving is within 0.5 steps. However, in FIG. 8, when the subject luminance varies from 4.6 to 5.6, the aperture is 1 from AV3 to AV4. There is a technical problem that even if the hysteresis width is set finely, the exposure shift does not change when the diaphragm moves greatly even if the hysteresis width is set finely.

An object of the present invention is to realize the appearance of a live view image by driving an aperture during moving image shooting and to improve the image quality of a recorded moving image without being affected by the operating characteristics of the diaphragm mechanism in the mounted lens. To provide a camera and a camera control method .

One aspect of the present invention is a camera capable of at least one of video shooting and live view display.
Imaging means for converting an image formed by the taking lens into an electrical signal;
Subject luminance acquisition means for acquiring subject luminance;
Exposure calculation means for calculating a shutter speed and an aperture value based on the subject brightness of the subject brightness acquisition means;
Shutter means for controlling the time during which the imaging means accumulates an optical signal based on the shutter speed output by the exposure calculating means;
A diaphragm control means for controlling a diaphragm aperture of the diaphragm means for limiting the amount of light incident from the photographing lens based on the diaphragm value output by the exposure calculation means;
Determining means for determining whether or not to change the aperture value of the aperture means;
Storage means for storing first information and second information different from each other, which are information relating to an amount of change in exposure in accordance with a deviation from an appropriate exposure amount;
With
The exposure calculation unit is configured to determine whether the previous exposure amount is appropriate based on the luminance information output from the subject luminance acquisition unit related to the previous exposure, the aperture value of the aperture unit, and the shutter speed of the shutter unit. When calculating the deviation from the exposure amount and calculating the aperture value of the aperture means at the next exposure based on the calculated deviation, the determination means determines to change the aperture value of the aperture means For calculating the aperture value at the next exposure so as to eliminate a part of the calculated deviation based on the first information output from the storage unit, and the determining unit determines the aperture value of the aperture unit. If it is determined not to change, the shutter speed at the next exposure is calculated so as to eliminate all of the calculated deviation based on the second information output from the storage means . Provide camera
Another aspect of the present invention is a camera control method that includes an imaging lens, an imaging unit, and a diaphragm unit that limits an amount of light incident from the imaging lens, and is capable of at least one of moving image shooting and live view display.
A first step of converting an image formed on the imaging means by the photographing lens into an electrical signal;
A second step of obtaining subject brightness based on the converted electrical signal ;
A third step of calculating a shutter speed and an aperture value based on the subject brightness obtained in the second step;
A fourth step of performing an exposure operation based on the shutter speed and the aperture value calculated in the third step ;
It includes,
In the third step, the brightness information obtained in the second step in relation to the previous exposure, the aperture value and the shutter speed calculated in the third step in relation to the previous exposure are determined. Based on the previous exposure amount and the appropriate exposure amount, and when calculating the aperture value of the aperture means at the next exposure based on the calculated deviation, When changing the value, the aperture value at the next exposure is calculated so as to eliminate a part of the calculated deviation, and when the aperture value of the aperture means is not changed, the calculated deviation is calculated. The camera control method is characterized in that the shutter speed at the next exposure is calculated so as to eliminate all of the above .

According to the present invention, it is possible to realize the appearance of the live view image by the aperture driving during moving image shooting and the improvement of the image quality of the recorded moving image without being affected by the operating characteristics of the diaphragm mechanism in the mounted lens. A camera and a camera control method can be provided.

It is a diagram which shows exposure control of the camera only for a moving image which is the reference technique of this invention. It is a diagram for explaining a technical problem of moving image shooting in a camera having an aperture mechanism optimized for still image shooting, which is a reference technique of the present invention. As a reference technique of the present invention, it is a program diagram showing the relationship between aperture driving, shutter speed, and luminance when no hysteresis is provided. FIG. As a reference technique of the present invention, it is a program diagram showing the relationship between aperture drive and luminance when no hysteresis is provided. FIG. FIG. 7 is a program diagram showing the relationship among aperture driving, shutter speed, and luminance when a hysteresis for one stage is provided as a reference technique of the present invention. It is a program diagram which shows the relationship between aperture drive and a brightness | luminance at the time of providing the hysteresis for 1 step | paragraph as reference technology of this invention. As a reference technique of the present invention, it is a program diagram showing the relationship among aperture driving, shutter speed, and luminance when a hysteresis of 0.5 steps is provided. As a reference technique of the present invention, it is a program diagram showing the relationship between aperture drive and luminance when a hysteresis of 0.5 steps is provided. FIG. It is a conceptual diagram which shows the structure of the camera which is one embodiment of this invention. It is a flowchart which shows an example of the basic operation | movement of the camera which is one embodiment of this invention. It is a flowchart which shows an example of the detail of the exposure parameter calculation process in the camera which is one embodiment of this invention. It is a diagram which shows an example of the brightness | luminance tracking speed control in the exposure parameter calculation process in the camera which is one embodiment of this invention. It is a program diagram which shows the hysteresis control example of AV value and TV value with respect to the brightness | luminance BV in the camera which is one embodiment of this invention. It is a diagram which shows an example of the relationship between the brightness | luminance and aperture_diaphragm | restriction in the hysteresis control of FIG. It is a diagram which shows the modification of the brightness | luminance tracking speed control in the exposure parameter process in the camera which is one embodiment of this invention. It is a diagram which shows the example of a setting of the aperture drive area | region of the function used by the brightness | luminance tracking speed control in the camera which is one embodiment of this invention. It is a diagram which shows an example of the relationship between a general imaging output, the moving image file recorded on a recording medium, and the digital data of an image file. It is a diagram which shows the example of a setting of the aperture drive area | region of the function used by the brightness | luminance tracking speed control in the camera which is one embodiment of this invention.

In this embodiment, in live view or moving image shooting in which an image output from the image sensor is displayed on a monitor, control is performed to suppress fluctuations in image brightness when the aperture is driven during moving image shooting. For example, it is effective for a lens having an aperture mechanism optimized for still image shooting.

If it is determined that the aperture value of the next exposure will be changed from the aperture value of the previous exposure, the response amount of the exposure control is changed to the brightness of the subject, thereby changing the aperture driving amount to be moved by one aperture drive. Suppress to the optimum value.

That is, in this embodiment, as an aspect, for example, even in a camera that cannot obtain an aperture value during aperture driving in shooting using images of continuous imaging operations such as live view display or moving image recording, In order to suppress brightness flicker, the aperture control hysteresis is configured to be, for example, about 1/6 step, and at the same time, in movie shooting, the aperture value set for the previous frame exposure and the aperture value set for the next frame exposure are different. When this is determined, the response speed of the exposure control with respect to the luminance variation of the subject is changed, so that the aperture drive amount that is moved by one aperture drive is controlled by the aperture drive amount according to the characteristics of the aperture mechanism.

As a result, for example, even when shooting using a lens with a step-driven aperture mechanism that is specialized for still images and not for moving image recording, exposure errors and fluctuation frequencies during aperture driving are reduced in moving image shooting. As a result, it is possible to suppress the flickering of brightness, and to improve the quality of the monitor display image of the live view and the quality of the recorded image in moving image recording while the response of the luminance fluctuation of the subject is appropriate.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 9 is a conceptual diagram showing a configuration of a camera according to an embodiment of the present invention. In this embodiment, as an example of a camera, a case where the present invention is applied to a digital single-lens reflex camera capable of exchanging lenses is illustrated.

The digital single-lens reflex camera (hereinafter simply referred to as “camera”) of the present embodiment records a body unit 100, an interchangeable lens unit (ie, a lens barrel) 200, and captured image data. A recording medium 131 is provided.

The lens unit 200 is detachable via a lens mount (not shown) provided on the front surface of the body unit 100, and is interchangeable with the camera.

The lens unit 200 includes photographing lenses 210a (photographing lenses) and 210b, a diaphragm 203 (aperture means), a lens driving mechanism 204, a diaphragm driving mechanism 202, and a lens control microcomputer (hereinafter referred to as Lμcom) 201. It consists of and.

The taking lenses 210a and 210b are driven in the optical axis direction by a DC motor (not shown) provided in the lens driving mechanism 204. The diaphragm 203 is driven by a stepping motor (not shown) provided in the diaphragm drive mechanism 202.

The Lμcom 201 controls driving of each part in the lens unit 200 such as the lens driving mechanism 204 and the diaphragm driving mechanism 202. The Lμcom 201 is electrically connected to a later-described body control microcomputer 101 (aperture control means) (hereinafter abbreviated as Bμcom101) via a communication connector 160, and can exchange various data with the Bμcom101. And is controlled by Bμcom 101.

On the other hand, the body unit 100 includes an image sensor 111 (subject luminance acquisition means) (imaging means), an image sensor drive IC 110 (shutter means) (sensitivity setting means), an image processing IC 102, an SDRAM 104, a shutter unit 120 ( Shutter means), a shutter drive control circuit 121, a communication connector 130, a liquid crystal monitor 140, a camera operation switch 150, a Bμcom 101, and the like.

A light beam from a subject (not shown) incident through the photographing lenses 210a and 210b and the diaphragm 203 in the lens unit 200 passes through the focal plane type shutter unit 120 on the optical axis and the optical system, and forms a subject image. The light enters the image sensor 111 for photoelectric conversion.

The light flux that has passed through the photographing lenses 210 a and 210 b forms an image on the image sensor 111 and the image sensor 111 in the image sensor drive IC 110. The image sensor 111 is photoelectrically controlled by the image sensor driving IC 110. The image sensor driving IC 110 controls the sensitivity of photoelectric conversion in the image sensor 111 based on an instruction from the Bμcom 101 or the like.

Then, the image sensor 111 photoelectrically converts the subject image formed as described above to convert it into an analog electric signal. The electric signal is converted into a digital electric signal to be processed by the image processing IC 102 by the image sensor driving IC 110 and converted into an image signal by the image processing IC 102.

In the body unit 100, an image sensor 111, an image sensor drive IC, an SDRAM (Synchronous Dynamic Random Access Memory) 104 provided as a storage area, a liquid crystal monitor 140, and a recording medium 131 via a communication connector 130 are provided. These are connected to an image processing IC 102 for performing image processing, and these are configured to provide an electronic recording display function together with an electronic imaging function.

The recording medium 131 is an external recording medium such as various semiconductor memory cards or an external hard disk drive (HDD), and is attached to the body unit 100 via the communication connector 130 so as to be exchangeable.

The image processing IC 102 is connected to a Bμcom 101 for controlling each part in the body unit 100. This Bμcom 101 has a timer (not shown) that measures the shooting interval during continuous shooting. In addition to the control means that controls the overall operation of the camera, the counting means, mode setting means, detection means, determination means, It has functions such as calculation means.

The Bμcom 101 is connected to the communication connector 160, the shutter drive control circuit 121, and the like, and further, a liquid crystal monitor 140 for notifying the photographer of the operation state of the camera by display output, and a camera operation switch (SW). 150 is connected to a power source (not shown).

Bμcom 101 and Lμcom 201 are electrically connected to each other via communication connector 160 by attaching lens unit 200 to body unit 100. The Lμcom 201 operates as a digital camera while cooperating with the Bμcom 101 in a dependent manner.

In this case, the Bμcom 101 controls the entire body unit 100 and the lens unit 200 as described above by executing a control program 170 stored in a non-illustrated nonvolatile semiconductor memory or the like, as shown in the flowchart described later. Realization of control operations.

The shutter drive control circuit 121 controls the movement of a front curtain and a rear curtain (not shown) in the shutter unit 120, and also controls a signal for controlling the opening / closing operation of the shutter with the Bμcom 101 and a signal when the front curtain completes traveling. Give and receive.

In the case of the present embodiment, in addition to the shutter unit 120, the image sensor driving IC 110 is provided with an electronic shutter function for moving image shooting. During moving image shooting, the shutter unit 120 is opened and the Bμcom 101 is used for electronic recording. The shutter speed of the shutter function is controlled.

At the time of still image shooting, for example, still image shooting is performed at a predetermined shutter speed by the operation of the shutter unit 120.
The liquid crystal monitor 140 is for notifying the user (photographer) of the operation state of the camera by display output.

The camera operation switch 150 is, for example, a release switch for instructing execution of a shooting operation, a mode change switch for switching a shooting mode to a continuous shooting mode or a normal shooting mode, a power switch for switching the power on / off, and the like. It is composed of a group of switches including operation buttons (operation means) necessary for the operation.

The body unit 100 is provided with a power supply circuit (not shown), and a voltage of a battery (not shown) serving as a power supply is converted into a voltage required for each circuit unit of the camera and supplied.

Although not shown in particular, the body unit 100 is provided with a microphone that detects external sound or the like, and the image processing IC 102 and the Bμcom 101 record sound together with the moving image obtained from the image sensor 111 to record media. 131 can be stored.

Next, shooting operation and live view operation by the camera of the present embodiment will be described.

<Shooting operation>
First, when the image processing IC 102 is controlled by the Bμcom 101 that executes the control program 170 and image data is input from the image sensor 111 and the image sensor drive IC 110 to the image processing IC 102, the image processing IC 102 temporarily stores the image data. The data is stored in the SDRAM 104 which is a storage memory.

The SDRAM 104 is also used as a work area for the image processing IC 102 to perform image processing. Further, the image processing IC 102 can perform image processing for converting the image data into a desired image data exchange standard (for example, JPEG data) and store the image data on the recording medium 131.

When the shutter drive control circuit 121 receives a signal for controlling the drive of the shutter from the Bμcom 101, the shutter drive control circuit 121 controls the shutter unit 120 to open / close the shutter. At this time, predetermined image processing is performed on the image data output from the image sensor 111 and the image sensor drive IC 110 and the result is recorded on the recording medium 131, whereby the still image shooting operation is completed.

<Live view operation and video recording>
The light beams from the photographing lenses 210 a and 210 b are guided to the image sensor 111 and the image sensor drive IC 110. For example, exposure is continuously performed at a rate of about 30 frames per second, and image data output from the image sensor 111 and the image sensor drive IC 110 at this time is converted into a video signal by the image processing IC 102 and liquid crystal By giving to the monitor 140, the moving image of the subject can be displayed on the liquid crystal monitor 140.

Such a display is called “live view” and is well known. In order to display the live view display of the image data on the liquid crystal monitor 140 with the camera of the present embodiment, the user selects the live view mode by operating the mode change switch in the camera operation switch 150 described above. do it. Hereinafter, the live view may be abbreviated as “LV”.

If a moving image file is generated by the image processing IC 102 and recorded on the recording medium 131 via the communication connector 130, moving image recording is performed. In order for the user to perform moving image recording, a switch provided on the camera operation switch 150 for starting and stopping moving image recording may be operated.

During the LV operation, the light flux from the photographing lenses 210a and 210b is always guided to the image sensor 111 and the image sensor drive IC 110. Therefore, subject brightness photometry processing and known distance measurement processing for the subject are performed. Based on the image data output from the image sensor 111 and the image sensor drive IC 110, the image processing IC 102 can perform the process.

Thereafter, in this way, subject brightness photometry processing, subject distance measurement and automatic focusing processing performed by the image processing IC 102 and the Bμcom 101 based on the image data output from the image sensor 111 and the image sensor drive IC 110 in this way. Are denoted as “LV metering” and “LVAF”, respectively, as necessary.

FIG. 10 is a flowchart illustrating an example of a basic operation of the camera according to the present embodiment.
FIG. 11 is a flowchart showing an example of details of exposure parameter processing in the camera of the present embodiment.

(Step S10 :)
When the body unit 100 recognizes that the lens unit 200 is connected when the power of the body unit 100 is turned on or when the lens unit 200 is connected, step S20 is performed.

(Step S20 :)
In the body unit 100 and the lens unit 200, a vertical synchronization signal of the image sensor 111 is transmitted from the body unit 100 to the lens unit 200 via the communication connector 160.

From the Lμcom 201 of the lens unit 200, information such as the aperture control speed, for example, the driving time required for driving the aperture one step is transmitted to the Bμcom 101 of the body unit 100. The predetermined aperture driving time may be transmitted from the Bμcom 101 of the body unit 100 to the lens unit 200, and the aperture amount that the Lμcom 201 of the lens unit 200 can move in the predetermined aperture driving time may be returned to the body unit 100.

In the case of the lens unit 200 that does not return information indicating the aperture driving speed, a large predetermined value is set as the aperture driving time.

(Step S30 :)
The photographic lens 210a and the image sensor 111 are driven and exposed at a predetermined aperture value, electronic shutter speed, and sensitivity for starting the live view operation described above.

(Step S40 :)
The subject brightness is calculated by the above-mentioned LV photometry from the imaging output obtained at the previous exposure, and the aperture value of the next exposure, the shutter time, and the sensitivity value are calculated according to the program diagram determined in advance according to the subject brightness. calculate.

In the present embodiment, by performing processing as shown in FIG. 11 to be described later showing a detailed example of this step S40, control is performed to reduce the variation of the aperture value as much as possible according to the luminance change of the subject in the LV. , It is possible to suppress flickering of an image in the LV and to present a good-looking LV image to the user.

(Step S50 :)
Exposure is performed by controlling the lens unit 200 and the image sensor 111 at the aperture value and the shutter speed of the electronic shutter calculated in step S40, and an image output P is obtained. The brightness of the subject is calculated from the obtained imaging output P, the set aperture value, and the shutter speed of the electronic shutter.

Here, if the aperture 203 is being driven while the image sensor 111 is exposed, the subject brightness is not calculated and the previous value is set as the subject brightness value.

(Step S60 :)
It is determined whether the release switch button of the camera operation switch 150 is turned on. If it is ON, the process proceeds to step S70, and if not, step S40 and step S50 are repeated during the live view.

(Step S70 :)
The image obtained in the live view is processed by the image processing IC 102 and recording on the recording medium 131 is started as a moving image.

(Step S80 :)
From the imaging output P obtained by the previous exposure, the aperture value, shutter speed, and sensitivity are calculated. This is the same processing as in step S40 described above.

(Step S90 :)
The lens unit 200 and the image sensor 111 are controlled to perform exposure at the aperture value and the shutter speed of the electronic shutter calculated in step S80, and an image output P is obtained. The brightness of the subject is calculated from the obtained imaging output P, the set aperture value, and the shutter speed of the electronic shutter.

(Step S100 :)
The state of the release button of the camera operation switch 150 is confirmed. When the release button pressed in step S60 is pressed again, the process proceeds to step S110. If not, the process returns to step S80, and automatic exposure is repeated until the release button is pressed again to continue recording a moving image. If the release button is pressed, the process proceeds to step S110.

(Step S110 :)
End movie recording. The image recording on the recording medium 131 is stopped, and the liquid crystal monitor 140 is notified that the moving image recording is stopped. After the recording is stopped, the normal live view state in which recording is not performed (step S30) is resumed.

After that, the actual camera returns to the start of the live view operation in step S30 and enters the release standby state. However, for the sake of simplicity, the description will proceed with the end of the camera operation after the completion of step S110.
Next, an example of the “exposure parameter determination” operation in steps S40 and S80 described above will be described with reference to FIG.

Still image exposure is determined using the APEX (Additive System of Photographic Exposure) calculation used in camera control technology, etc.
BV: Brightness Value
SV: Sensitive Value
AV: Aperture Value
TV: Exposure time (Time Value)
When the traditional notation is used, AV, TV, and SV used for photographing with appropriate exposure when the subject brightness BV is obtained are controlled so that the relationship of the following expression (1) is satisfied.
BV + SV = AV + TV (1)

In moving image shooting, from the imaging output P obtained at the previous exposure, the AV, TV, SV set at this exposure, and the imaging output appropriate level P ₀ ,
BV = AV + TV + SV + Log ₂ (P / P ₀ ) (2)
It is calculated by the calculation.
Since the imaging output P is generally an output value proportional to the illuminance, a logarithm with a base of 2 is taken, and the number of steps corresponding to the difference from the appropriate level is replaced with a unit system of “stage”.
Basically, the next exposure is performed using AV, TV, and SV that make the BV value appropriate.

However, in the present embodiment, as necessary, the exposure parameter is controlled to be moderately appropriate over a plurality of frames by suppressing the change of the exposure parameter. This exposure parameter control in the present embodiment controls the speed of the follow-up in the operation of causing the exposure value to follow the change in the subject brightness in order to make the camera exposure appropriate for the change in the subject brightness. In this sense, it is called the luminance tracking speed.

Since still photography basically pursues high speed (that is, a small release time lag), it is required to react swiftly to luminance fluctuations of the subject.
From the appropriate condition of the formula (1), which is a known relational expression,
BV + ΔBV + SV ≠ AV + TV (3)
Thus, it deviates from the appropriate condition by ΔBV.
In the case of agile response, in the next exposure control, simply changing the exposure parameter composed of ΔBV, the aperture value, the shutter speed, and the sensitivity provides an appropriate exposure level.

On the other hand, as in the present embodiment, when it is intended to respond gently to the luminance variation of the subject during moving image shooting, the exposure parameter is changed to less than ΔBV in the next exposure control.

FIG. 12 is a graph showing the control of the luminance tracking speed. The vertical and horizontal axes of the graph are described as absolute values. If the exposure deviation amount ΔBV is negative, _{ΔBV_next on} the vertical axis is also negative. For example, in the solid line graph C0, when the horizontal axis ΔBV is −2, The axis _{ΔBV_next} becomes −2. Similarly, when ΔBV is +2, _{ΔBV_next} is expressed as +2.

The horizontal axis uses ΔBV as a value indicating how much the exposure is from the appropriate condition. The vertical axis indicates how much of the exposure amount shifted in the next exposure is properly adjusted.
A solid line graph C0 shows exposure control performed when the aperture is not driven (aperture non-fluctuation region).

The dotted line graph C1 is an example of luminance follow-up control when it is determined to change the aperture value set at the next exposure from the aperture value at the previous exposure (aperture variation region) as in the present embodiment. Show.

AV exposure parameters currently set respectively _{_{_now,}} TV _{_now,} and _SV _now. Let _{Bv_now} be the BV value obtained with the currently set exposure. AV exposure parameter to be set next respectively _{_{_next,}} TV _{_next,} and SV _{_next.} That is, _{AV_next} is a change amount of the aperture value.
The appropriate brightness _{BV_calc} with the exposure parameters set this time is
_{_{_{BV _calc = AV _now + TV _now}}} -SV _now ...... (4)
It is defined as

When the luminance variation of the subject occurs, the amount of deviation ΔBV from the appropriate level is obtained from the BV value acquired this time.
_{_{ΔBV = BV _now -BV _calc ...... (}} 5)
This ΔBV is a parameter on the horizontal axis in FIG.

_{ΔBV_next on the} vertical axis is a value for calculating _{BV_next} , which is a value for determining the next exposure parameter,
_{BV_next} = _{BV_calc} + _{ΔBV_next} (6)
In this embodiment, the AV value, the TV value, and the SV value are determined so that the luminance _{BV_next} becomes appropriate at the next exposure.

When _{ΔBV_next} is smaller than ΔBV, for example, ΔBV is −1 step, indicating that the current exposure is one step under, and when _{ΔBV_next} is −0.5 step, the next exposure is 0. The movement is controlled so as to be under 5 steps.

In this way, in the present embodiment, the control of the dotted line graph C1 in FIG. 12 is realized, and details will be described in the description of the flowchart in FIG.

Next, the aperture driving area and the non-varying area will be described.
FIG. 13 is a program diagram showing control of AV value and TV value with respect to luminance BV in the present embodiment. In general, a diagram of the BV value and the SV value is also added here, but for the sake of simplification of description, the description will be made on the assumption that the SV value is fixed at a constant SV _c (in this case, SV _c = 5).

In the program diagram of the present embodiment illustrated in FIG. 13, hysteresis is configured in the control of the AV value and the TV value. The hysteresis shape is such that the TV value is long and the AV value is short.

That is, in the present embodiment, the TV value is changed as much as possible without changing the AV value in a predetermined control range of the TV value (in the setting example of FIG. 13, _{TV_min} = 5 to _{TV_max} = 7). Control is performed so as to maintain the relationship of the expression (1) by changing the value, and when the TV value is likely to deviate from the predetermined control range, the AV value (in this case, AV _{_min} = 3.0 to be described later) The control is performed to change (between _{AV_max} = 4).

The diaphragm 203 is opened when the state of the diaphragm is darker than the TV = _{TV_min} (in this case, 5) (first shutter speed). Similarly, on the brighter side, the aperture 203 is closed when the aperture state is a bright brightness where the TV value is larger than TV = _{TV_max} (7 in this case) (second shutter speed). .

FIG. 14 is a diagram showing an example of the relationship between the brightness and the aperture in the present embodiment. Hysteresis is configured so that the difference between the luminance that increases the AV value and the luminance that decreases is increased. The aperture driving area (graph C1) is an area for determining that the aperture value at the previous exposure differs from the aperture value set at the next exposure. Details are described below with reference to the flowchart of FIG. explain.

Next, an example of “exposure parameter determination” processing in the aperture driving region (graph C1) will be described with reference to FIG.

(Step S210 :)
As described above, an appropriate brightness _{BV_calc} is obtained using the exposure parameter obtained when the obtained imaging output P is set.
_{_{_{BV _calc = AV _now + TV _now}}} -SV _now ...... (7)
_{BV_now} calculated from the actually obtained imaging output P obtains ΔBV indicating the amount of deviation from the appropriate level from the BV value acquired this time.
_{_{ΔBV = BV _now -BV _calc ...... (}} 8)
When the calculation is completed, the process proceeds to step S220.

(Step S220 :)
First, it is treated as an aperture non-drive region, and _{BV_next,} which is a source for determining the next exposure parameters AV, Tv, and SV, is determined by the following equation (9).
_{BV_next} = _{BV_calc} + F (ΔBV) (9)
In the flowchart of FIG. 11, a general notation function F () is described as the graph C0.

This indicates that, in the present embodiment, a solid line graph C2 in FIG. 15 can be used as an example. That is, it is shown that the control of the present embodiment can be used even when the response speed of exposure is always gradual.

Actually, it is conceivable that F () of the graph C0 is an appropriate function so that the luminance tracking speed of the aperture driving area (graph C1) and the luminance tracking speed of the aperture non-driving area (graph C2) are not too different. In this embodiment, the description will be given taking the case of FIG. 12 as an example. If calculation of (9) Formula is completed, it will progress to step S230.

(Step S230 :)
Determine if the current exposure is under.

_{BV_next} indicating the appropriate brightness for the next exposure is compared with the appropriate brightness _{BV_calc} for the exposure parameter when the current imaging output P is obtained. If _{BV_next} is small, the exposure parameter is _adjusted to a dark subject. . That is, at least one of opening the aperture 203, extending the shutter speed of the electronic shutter, and increasing the sensitivity is controlled.

If the current exposure is under, the process proceeds to step S250. If the current exposure is not under, the process proceeds to step S240.

(Step S240 :)
Contrary to step S230, it is determined whether or not the current exposure is over.
When _{BV_next} is larger than _{BV_calc, the exposure} is _{adjusted to be} more suitable for the higher luminance side than the present, and at least one of driving the diaphragm 203 to the closing side, shortening the shutter speed, and lowering the sensitivity is controlled. Will do.

If the current exposure is overside, the process proceeds to step S300. If the current exposure is not overside, that is, if it is appropriate, the process proceeds to step S350.

(Step S250 :)
When _{BV_next} < _{BV_calc} is satisfied in step S230 described above and the brightness _{BV_next} is appropriate, it is determined whether the TV value is smaller than 5 when only the shutter speed is changed with the current aperture value.
The current aperture value _{AV_now} , sensitivity SV value (described below with SV _c = 5), and _{BV_next} are used for determination.

Judgment is made by equation (10) to which the equation (1), which is a conditional equation for obtaining appropriate exposure, is applied.
_{_{_{BV _next + SV c <AV _now}}} + TV _min ...... (10)
If this equation (10) is satisfied, it indicates that the TV value is smaller than _{TV_min} (in this case, _{TV_min} = 5) unless the aperture 203 is changed in the opening direction, and the process proceeds to step S260.

Here, the meaning of the determination of changing the aperture to the opening direction when the TV value is smaller than _{TV_min} unless the aperture is changed will be described.
As illustrated in the program diagram of FIG. 13 described above, the camera generally selects and determines AV, TV, and SV from the BV value according to the program diagram.

In the present embodiment, the control of opening the diaphragm 203 only when the TV value is smaller than _{TV_min} is for realizing the control by the program diagram having the hysteresis of FIG. The program diagram with hysteresis is as described in FIGS. 3, 4, 5, 6, 7, and 8.

In this embodiment, since the SV value is fixed to SV _c = 5, the discussion proceeds, and FIG. 13 shows the relationship among the AV value, the TV value, and the BV value. The vertical axis represents the AV value, and the horizontal axis represents the TV value. Diagonal lines indicate luminance.

In step S300, which will be described later, according to the equation (15), when the TV becomes larger than _{TV_max} (in this case, _{TV_max} = 7), the diaphragm 203 is set in the direction of narrowing down, thereby forming a hysteresis of about two stages. .

If this equation (10) is not satisfied, it is determined that it is not necessary to change the aperture because the TV value is larger than _{TV_min} (in this case, _{TV_min} = 5) without changing the aperture. Proceed to S350.

(Step S260 :)
_{AV_min} (in this case, _{AV_min} = 3.0) is the smallest aperture value in the driving range in which the aperture is used in a predetermined moving image. _{AV_min} is determined by the design concept such that the AV value when the diaphragm 203 is _fully opened cannot be physically reduced, or the depth of field is not too shallow for the convenience of the camera, for example.

When the currently set aperture value is _{AV_min} , the aperture 203 is not opened any more, and the TV value is set to less than _{TV_min} to be appropriate. Therefore, it is determined that the diaphragm 203 is not driven and the process proceeds to step S350.
If the currently set aperture value is not _{AV_min} , the process proceeds to step S270.

(Step S270 :)
When all of the determination conditions of steps S230, S250, and S260 are satisfied, it is necessary to control to open the aperture 203 from the current aperture value at the next exposure. That is, it is considered that the aperture driving area (graph C1) in FIG. 12 has been determined.

In order to set the luminance follow-up speed slower, _{BV_next} is _{recalculated,} and the change amount from _{BV_calc} is reduced by the following equation (11) based on ΔBV which is a deviation from the appropriate exposure level.
_{BV_next} = _{BV_calc} + G (ΔBV) (11)
The function G (ΔBV) that gives _{ΔBV_next} is a function that realizes control of the dotted line graph C1 in FIG. 12, and is realized or approximated in a table reference format storing the relationship of _{ΔBV_next} to ΔBV as shown in FIG. It is calculated by function. The function G () is calculated so that the absolute value of G (ΔBV) is kept smaller than ΔBV.

In the present embodiment, by suppressing the luminance follow-up speed by such calculation, the aperture amount driven by one aperture drive calculated in the operations of steps S280 and S290 described later can be suppressed and occurs during aperture drive. The amount of exposure shift will also be suppressed. As a result, good moving image shooting with less flickering is realized even during aperture driving.

Further, in order to suppress flickering, suppressing the amount of fluctuation of the aperture value unnecessarily slows down the luminance follow-up speed, and there is a case where the composition cannot be confirmed without subjecting exposure to a subject with large luminance fluctuation.

Therefore, in the present embodiment, as seen from the dotted line graph C1 in FIG. 12, the amount _{ΔBV_next} to follow the luminance increases as the exposure deviation amount ΔBV from the appropriate level increases. Thereby, when the exposure is greatly deviated, the aperture value moves greatly, and the exposure can be accurately followed even for a subject with a large luminance fluctuation.

FIG. 17 shows a relational expression between the general imaging output P and the digital data of the moving image file and the image file recorded on the recording medium. This curve C3, generally called a gamma curve, is used when converting the imaging output P to the format of a moving image file.

In order to convert to a data format with a smaller data amount than the imaging output P, the data of the image file is compressed even if the imaging output P changes by ΔDig by compressing the data in the area where the imaging output P is small and large. The change amount ΔDig ′ is set to a smaller change amount.

In this way, the information that the imaging output P has is stored in the image file with a large amount of information of gradation near the appropriate level of the imaging output P. The same can be said for the live view display that attempts to reproduce the image file recorded at the time of shooting.

In this way, in the area away from the appropriate level of the imaging output, the final image output is compressed, so that the exposure deviation during driving of the aperture is relatively inconspicuous in the compressed area compared to the appropriate time of imaging.

Therefore, in this compression area, priority is given to the luminance follow-up speed, and control is performed to move the aperture largely. This control alleviates the problem that the composition cannot be confirmed for a long time when the exposure does not match, and instead of slowing down the brightness tracking speed when the composition is close enough to confirm the composition, the aperture is adjusted so that the flicker is not noticeable. By adjusting the driving amount little by little, it is a movement that makes it possible to achieve both luminance tracking and flicker prevention.

Further, in the present embodiment, as shown in FIG. 16, when the absolute value of the deviation amount ΔBV is 3 or more, the driving amount of the diaphragm that is moved at a time is set to 1.5. In addition to the problem that the flicker is conspicuous, if the driving amount of the diaphragm is large, the driving time of the diaphragm becomes long, and there is an effect of reducing the frequency at which an image in which the exposure during driving of the diaphragm is shifted appears in a plurality of frames.

For example, in an interchangeable lens camera, the numerical value of 1.5 steps may be changed according to the driving speed of the diaphragm mechanism provided in the attached lens. For example, in the case of a lens with slow aperture driving, it can be considered that control is performed so that _{ΔBV_next} is a maximum of one stage.

In other words, by setting the optimum brightness follow-up speed for the aperture characteristics, the quality of the moving image and the brightness follow-up speed can be controlled in an optimum state (balance).
When the _{recalculation} of _{BV_next} is completed, the process proceeds to step S280.

(Step S280 :)
In step S280, the aperture value to be set next time is calculated.
In order to determine the aperture value at a predetermined change step (in this case, 0.2 stage resolution), the following equation (12) is calculated.
_{n = (BV _next - (AV} _min + TV _min -SV c)) ÷ 0.2 ...... (12)
n is rounded down. If n ≦ 0, n = 0. Then, the aperture value to be set next time is calculated by the following equation (13). In this case, however, _{AV_min} = 3.
_{_{AV _next = AV _min + 0.2 ×}} n ...... (13)
The reason why the change step is 0.2 resolution in the equation (13) is that hysteresis is constituted by the aperture and the shutter speed.
The component corresponding to the luminance represented by ( _{AV_min} + _{TV_min−} SV _c ) in Expression (12) is appropriate exposure when the aperture is most open (AV = _{AV_min} ) and the TV value is _{TV_min.} It shows luminance.
Expression (12) shows that the amount of change in the aperture value for increasing the AV value from _{AV_min} to an appropriate exposure by 0.2 as much as _{BV_next} is brighter than the brightness at which the appropriate exposure is obtained when the aperture is most opened. This is a calculation for determining the number of steps in each step.
Therefore, “0.2 × n” in Expression (13) indicates the amount of change in the aperture value.

The reason for the truncation decimal point in the calculation of the TV _{_next} performed in the next step S290, TV _{_next} is TV _{_min} (in this case, 5) in order so as not to fall below a.

By reducing the difference between _{BV_next} and _{BV_calc in} the preceding step S270, the amount of change in the AV value may be less than 0.2 and the aperture may be the same as _{AV_calc.} Instead of changing the luminance follow-up speed by step S230, S350, S260, the frequency of changing the brightness follow-up speed does not become too high when the brightness follow-up speed is determined by determining whether or not it is the aperture drive region. The image display on the screen looks good.

(Step S290 :)
Using the BV value and AV value determined in steps S270 and S280, the TV value of the next exposure parameter, _{TV_next,} is calculated using equation (14).

_{_{_{Tv _next = Bv _next + SV c}}} -AV _next ...... (14)
With this calculation, the aperture parameter, the shutter speed, and the sensitivity, which are the next exposure parameters when driving to the aperture driving area (graph C1) and the aperture 203 opening side, have been determined, and the exposure parameter processing is terminated.

(Step S300 :)
When the brightness _{BV_next} is made appropriate without changing the aperture, it is determined whether the TV value indicating the shutter time is larger than 7.
The current aperture value _{AV_now} , sensitivity SV value (in this case, fixed to SV _c = 5), and _{BV_next} are used for determination.
That is, the determination is made by the following equation (15) using the relationship of the above-described equation (1), which is a conditional equation for obtaining appropriate exposure.
_{_{_{BV _next + SV c> AV _now}}} + TV _max ...... (15)
If this equation (15) is satisfied, it means that the TV value will be larger than _{TV_max} (in this case, _{TV_max} = 7) unless the diaphragm 203 is changed in the closing direction, and the process proceeds to step S310.

The determination made here to change the aperture 203 only when the TV value is larger than _{TV_max} is to configure hysteresis as described in step S250 above.

If this equation (15) is not established, it indicates that the TV value is larger than _{TV_min} (in this case, _{TV_min} = 5) without changing the aperture, so it is determined that there is no need to change the aperture. Proceed to step S350.

(Step S310 :)
_{Let AV_max be} the largest aperture value in the drive range in which the aperture is used in predetermined moving image shooting. _{AV_max} is determined by the design concept such that the AV value when the diaphragm 203 is most narrowed cannot be physically increased, or the resolution is not lowered due to the diffraction limit, for example, for the convenience of the camera.

When the currently set aperture value is the largest aperture value within the driveable range of the aperture 203 used in the live view, the TV value is set to _{TV_max} (in this case, _{TV_max} = 7) The above is appropriate. Therefore, it is determined that the diaphragm 203 is not driven, and the process proceeds to step S350.

Aperture value AV _{_Now} currently set, if not the AV _{_max,} the process proceeds to step S320.

(Step S320 :)
In steps S240, S300, and S310, in the next exposure, it is necessary to control from the current aperture value to a method of closing the aperture 203. That is, it is considered that the aperture driving area (graph C1) in FIG. 12 has been determined.

In order to set the luminance tracking speed slower, _{BV_next} is _{recalculated,} and the amount of change from _{BV_calc} is reduced by the following equation (16).
_{BV_next} = _{BV_calc} + H (ΔBV) (16)
A function H (ΔBV) that gives _{ΔBV_next} from ΔBV is a function that realizes the dotted line graph C1 in FIG. 12, and is realized in a table reference format storing the relationship of _{ΔBV_next} to ΔBV as shown in FIG. It can be obtained with an approximate function. The function H () is calculated so that the absolute value of H (ΔBV) is smaller than ΔBV.

In the present embodiment, the difference from the function G (ΔBV) described in step S270 described above is only the sign, and the aim of this control is as described in step S270.
In the present embodiment, for simplicity of explanation, the dotted line graph C1 of FIG. 12 showing the function H () is represented in the same way as the function G () described above.

As a supplement, here, when the image is displayed brightly for a moment due to an exposure shift during aperture driving and when it is displayed darkly, flickering is more conspicuous when the image is displayed brightly.

The reason why the image is brightened for a moment is considered to be because the user feels dazzling and the unsightly is different. Therefore, the absolute value of the function H (ΔBV) in step S320 may be made larger than the absolute value of the function G (ΔBV) in step S270 described above to make the luminance tracking speed faster. it can.

When _{BV_next} in the aperture driving area is calculated, the process _proceeds to step S330.

(Step S330 :)
In step S330, the aperture value to be set next time is calculated.
In order to determine the aperture value with 0.2 stage resolution, the following equation (17) is calculated.
_{n = ((AV _max + TV} _max -SV c) -BV _next) ÷ 0.2 ...... (17)
In this equation (17), n is rounded down. If n ≦ 0, n = 0. Then, the aperture value to be set next time is calculated by the following equation (18). In this case, however, _{AV_max} = 4.
_{_{AV _next = AV _max -0.2 × n}} ...... (18)
The unit of change width is set to 0.2-step resolution as described in step S280 above.

The reason for the n truncate the decimal point, in the calculation of the TV _{_next} performed in the next step S340, when AV _{_next} is of less than AV _{_max,} TV _{_next} is TV _{_max} by an error caused by 0.2 step resolution (in this case This is so as not to exceed _{TV_max} = 7).

In step S320, that has a small difference in BV _{_next} and _BV _calc, although the aperture amount of change in AV value becomes less than 0.2 stage also be the same as the AV _{_Calc,} the above steps are also ideas This is the same as the description in S280.

In this step S330, _{AV_next} is determined. If calculation of (18) Formula is completed, it will progress to step S340.

(Step S340 :)
Using the BV value and AV value determined in steps S320 and S330, the next exposure parameter TV value, _{TV_next,} is calculated by the following equation (19).
_{_{_{Tv _next = Bv _next + SV c}}} -AV _next ...... (19)
With this calculation, since the aperture, shutter speed, and sensitivity, which are the next exposure parameters when driving to the aperture drive area and the aperture stop side, are determined, the exposure parameter processing is exited.

(Step S350 :)
If _{BV_calc} and _{BV_next} are the same in steps S230 and S240 and there is no need to change the exposure, if it is determined in steps S250, S260, S300, and S310 that the aperture is not driven (graph C0), the aperture 203 since it is determined not to move the, used as the current aperture value AV _{_Now} the AV _{_next} the next exposure. That is, the equation (20) is used.
_{_{AV _next = AV _now ...... (20}} )

As for the luminance follow-up speed, the TV value and the SV value are calculated by the above formula (14) using the value calculated in step S220.
If the aperture is not changed in step S350, the next exposure parameter aperture, shutter speed, and sensitivity have been determined, and the exposure parameter processing is exited.

The above is the description of the flowchart of FIG. 11 showing a detailed example of determining the exposure parameter in step S40 and step S80 of FIG.
With the exposure parameters obtained here set in step S50 or step S90 in FIG. 10, the display of LV images and the exposure of moving image recording are controlled.

By returning to step S40 and step S80 in the above-described step S60 and step S100, a continuous moving image is generated by repeating the operation of calculating the exposure parameter again.

At this time, in the case of the present embodiment, in the exposure parameter calculation method, the brightness follow-up speed is calculated and the hysteresis in which the AV value is finely cut is configured. By moving the aperture in small increments, the brightness flickering that occurs during aperture drive is suppressed, the image quality of LV images and recorded movies is improved, and when the exposure is under or over, brightness is driven by driving the aperture relatively large. The configuration is such that the speed is increased and a photo opportunity is not missed during still image shooting during LV display.

In the above embodiments, the SV value is fixed (in this case, SV = SV _c = 5). However, if the SV value is made variable in the program diagram of FIG. It is also easily known that the frequency of driving the diaphragm 203 can be further suppressed in the case of a subject that repeats light and dark.

For example, in step S250, the SV value is calculated as SV _c = 5 constant under the condition that the TV value is lower than _{TV_min} (in this case, _{TV_min} = 5). However, the SV value can be changed up to SV8 by the camera. In the system, the calculation formula (formula (10)) in step S250 may be changed to the following formula (21) with SV _c = 8.
_{_{BV _next + 8-AV _now <}} TV _min ...... (21)
If it does so, it will become the operation | movement which does not drive to the direction which the aperture_diaphragm | restriction 203 opens unless it becomes darker.

And after calculation of the step S290, S350 of FIG. 11, (in this case, TV _{_min} = 5) TV _{_next} is TV _{_min} If less than, and the TV _{_next} the TV _{_min,} the SV value, the following (22 )
_{_{_{SV _next = BV _next + TV _min}}} -AV _next ...... (22)
It is sufficient to add a process for calculating.

As described above, according to the present embodiment, the hysteresis that prevents the diaphragm 203 from operating as much as possible by changing the sensitivity (SV) and the shutter speed (TV) with priority over the diaphragm value (AV). A program diagram with characteristics is set, the amount of aperture change is changed according to the difference between the target exposure level and the current exposure level, and the luminance follow-up speed is changed between the aperture drive area and the non-aperture drive area. By changing, the rapid fluctuation (flickering) of the brightness of the video due to live view is suppressed.

As a result, for example, in a lens-interchangeable camera equipped with a live view function for confirming a composition with an image output from the image sensor 111, for example, a step drive type aperture drive mechanism 202 and an aperture optimized for still image shooting Even when the lens unit 200 having 203 is attached, it is possible to prevent the appearance of the live view image due to flickering of the live view image due to the aperture driving during moving image shooting and the deterioration of the image quality of the recorded moving image.

That is, according to the embodiment of the present invention, the appearance of the live view image by the aperture driving during moving image shooting and the recorded moving image are not affected by the operation characteristics such as the step operation of the diaphragm mechanism in the mounted lens. Image quality can be improved.

In addition, by setting the optimal brightness follow-up speed for the aperture characteristics, it is possible to control the quality of the video and the brightness follow-up speed in an optimal state (balance). It is possible to achieve both improvement in image quality and improvement in performance of still image shooting by shortening the release time lag in still image shooting with composition confirmation by live view.

Furthermore, since the operating frequency and operating speed of the aperture drive mechanism are reduced during moving image shooting with live view, the operating noise of the aperture drive mechanism during movie shooting is reduced and recorded together with the moving image quality along with the moving image. Sound quality is also improved.

Needless to say, the present invention is not limited to the configuration exemplified in the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, the configuration of the camera is not limited to the configuration exemplified in the above embodiment.

100 Body unit 101 Bμcom
102 Image processing IC
104 SDRAM
110 Image sensor drive IC
111 Image sensor 120 Shutter unit 121 Shutter drive control circuit 130 Communication connector 131 Recording medium 140 Liquid crystal monitor 150 Camera operation switch 160 Communication connector 170 Control program 200 Lens unit 201 Lμcom
202 Diaphragm drive mechanism 203 Diaphragm 204 Lens drive mechanism 210a Shooting lens 210b DC motor

Claims

In cameras that can perform at least one of video recording and live view display,
Imaging means for converting an image formed by the taking lens into an electrical signal;
Subject luminance acquisition means for acquiring subject luminance;
Exposure calculation means for calculating a shutter speed and an aperture value based on the subject brightness of the subject brightness acquisition means;
Shutter means for controlling the time during which the imaging means accumulates an optical signal based on the shutter speed output by the exposure calculating means;
A diaphragm control means for controlling a diaphragm aperture of the diaphragm means for limiting the amount of light incident from the photographing lens based on the diaphragm value output by the exposure calculation means;
Determining means for determining whether or not to change the aperture value of the aperture means;
Storage means for storing first information and second information different from each other, which are information relating to an amount of change in exposure in accordance with a deviation from an appropriate exposure amount;
With
The exposure calculation unit is configured to determine whether the previous exposure amount is appropriate based on the luminance information output from the subject luminance acquisition unit related to the previous exposure, the aperture value of the aperture unit, and the shutter speed of the shutter unit. When calculating the deviation from the exposure amount and calculating the aperture value of the aperture means at the next exposure based on the calculated deviation, the determination means determines to change the aperture value of the aperture means For calculating the aperture value at the next exposure so as to eliminate a part of the calculated deviation based on the first information output from the storage unit, and the determining unit determines the aperture value of the aperture unit. If it is determined not to change, the shutter speed at the next exposure is calculated so as to eliminate all of the calculated deviation based on the second information output from the storage means . camera.
The camera according to claim 1 , wherein the determination unit determines to change the aperture value when a shutter speed related to a next exposure amount exceeds a predetermined range.
Furthermore, it has sensitivity setting means for setting the sensitivity of photoelectric conversion with respect to the amount of light received by the imaging means,
The camera according to claim 1 , wherein the determination unit determines to change the aperture value when a sensitivity related to a next exposure amount exceeds a predetermined range.
In a control method for a camera having a photographing lens, an imaging means, and a diaphragm means for limiting the amount of light incident from the photographing lens, and capable of at least one of moving image shooting and live view display,
A first step of converting an image formed on the imaging means by the photographing lens into an electrical signal;
A second step of obtaining subject brightness based on the converted electrical signal ;
A third step of calculating a shutter speed and an aperture value based on the subject brightness obtained in the second step;
A fourth step of performing an exposure operation based on the shutter speed and the aperture value calculated in the third step ;
It includes,
In the third step, the brightness information obtained in the second step in relation to the previous exposure, the aperture value and the shutter speed calculated in the third step in relation to the previous exposure are determined. Based on the previous exposure amount and the appropriate exposure amount, and when calculating the aperture value of the aperture means at the next exposure based on the calculated deviation, When changing the value, the aperture value at the next exposure is calculated so as to eliminate a part of the calculated deviation, and when the aperture value of the aperture means is not changed, the calculated deviation is calculated. A camera control method characterized by calculating a shutter speed at the next exposure so as to eliminate all of the above .